This invention relates to a printing device provided with a function for printing and correcting character in bold face and the like by printing the characters in an overlapping state, more particularly, to a printing device having a function capable of attenuating an inconvenient vibration of a carriage at a printing position.
As shown in FIG. 1, a conventional printing device being excited and controlled two-two phase excitation provided with a function for printing character in bold face and the like employs such a printing method that a first print 1P is carried out when a carriage is stopped at a first stop position 1S (a two-phase exciting position of a step motor which reciprocates the carriage along a print line of a print sheet to be printed thereon), a second print 2P is carried out when the carriage is stopped at a second stop position 2S (an one-phase exciting position of the step motor), then a third print 3P is carried out when the carriage is stopped at a third stop position 3S (an one-phase exciting position of the step motor) which is symmetrical to the second stop position 2S about the first stop position 1S, and further a fourth print 4P is carried out at the same position as the third stop position 3S.
However, it is necessary for finely moving the carriage to employ a high-quality step motor having a high resolution, or general purpose step motor having an ordinary resolution with a large gear ratio for transmitting a drive power from the step motor to the carriage. Therefore, in a prior art, it is difficult to make the printing device inexpensive or to minimize a carriage driving system.
It may be considered that an one-two phase excitation operation is applied to the general purpose step motor for finely moving the carriage. A problem described later, however, may be occured by means of a difference of a torque value between a one-phase excitation and two-phase excitation when the one-two phase excitation operation is applied to the general purpose step motor as it is, it has not been applied for controlling the carriage so as to move finely in a bold-face print and a cerrection print operation.
If the above one-two phase excitation is applied when the bold-face print are executed, the problem described below may be occured.
When the carriage traveling at a high speed stops abruptly at the first stop position 1S to carry out the first print 1P, this printing operation is carried out while the carriage vibrates at the first stop position and thus the first print position may be dislocated. In addition, when the carriage is moved to the second print position by exciting an one-phase of the step motor after the first printing operation is finished, the carriage remains vibrated by the printing operation effected for the first print. Because the carriage can not be accurately moved to the second print position by the driving force produced by exciting the one-phase having smaller torque, the printing device has a problem in that a gap is caused between a first dint and second dint respectively printed by the first and second printing operation, the character is made very thick, or conversely it is made very thin.